This invention relates generally to vacuum type cleaning machines and more particularly concerns back-flow valves and valve triggers facilitating cyclical washing of the cleaning machine filters.
Back flow valves typically employ gates which are directly mechanically or electrically driven. Consequently, the speed of movement of the gate is governed throughout its range of motion. The result is a response time that is detrimental to the smooth operation of the machine, the filtering action being blocked for unnecessarily long intervals because of the slow response of the back-flow valve. Furthermore, these mechanical and electronic systems are extremely complex and expensive and available only on the most expensive cleaning machines. For lower priced equipment, down time for filter replacement or cleaning is required.
In one valve system disclosed in U.S. Pat. No. 4,618,352 to Nelson, cams within the system air ducts rotate in direct physical contact with their valve gates, holding the gates in horizontal planes until notches in the cams allow them to rotate into diagonal planes. This system has serious power and efficiency problems. First of all, the cams are disposed on a common shaft. The common shaft arrangement of the cams requires side-by-side alignment of the system ducts transverse to the common shaft. This adds to duct length and imposes location requirements which increase system losses and structural complexity. Second, the notches are angularly displaced on the cams to synchronize the operation of the gates. Since the gates are in direct contact with the cams, the notches must be relatively wide in order for the gates to open for a sufficient interval. This imposes limitations on the blower to vacuum time ratios which greatly reduce the efficiency of the system. Third, in the horizontal condition the gates completely seal the openings to the blower ducts. However, in the diagonal condition only the free ends of the gates engage the vacuum ducts, so that there is no seal and air loss occurs. Fourth, since the cam notches receive the gates, the cam diameters must be greater than the ducts the gates close. Consequently, for the gates and cams to maintain physical contact, the ducts must be slotted to receive the cams. Therefore, special housings are required to prevent further air losses in the system. Fifth, the cams are constantly driven so that the back-flow cycle occurs throughout the cleaning process, reducing the normal operating efficiency of the system. Sixth, because there is no seal during the vacuum process, the speed of operation of the gate is left essentially to an initial push by the blower and the force of gravity rather than taking advantage of the vacuum to help slam the gate home. Seventh, the blower and the vacuum share a common shaft, so the blower is operating unnecessarily throughout the vacuum process. The composite result of these individual problems is that the system is ineffective for cleaning at any appreciable distance from the machine.
It is, therefore, an object of this invention to provide a back-flow valve and valve trigger which facilitate cyclical washing of the cleaning machine filters. Another object of this invention is to provide a back-flow valve and valve trigger which have a rapid response time so as to limit the duration of the back flow interval. A further object of this invention is to provide a back-flow valve and valve trigger using a gate which is air-flow biased by both a blower and a vacuum source toward a back-flow condition. Yet another object of this invention is to provide a back-flow valve and valve trigger using a gate which is not mechanically controlled during its transition from normal operation to back-flow operation. It is also an object of this invention to provide a back-flow valve and valve trigger using a gate which is not electrically controlled during its transition from normal operation to a back-flow operation. Still another object of this invention is to provide a back-flow valve and valve trigger using a gate which is not governed during its transition from normal operation to back-flow operation. Another object of this invention is to provide a back-flow valve and valve trigger which do not unnecessarily increase the length of the internal duct system. Another object of this invention is to provide a back-flow valve and valve trigger which eliminate openings and gaps which would cause pressure losses in the system. Still another object of this invention is to provide a back-flow valve and valve trigger in which an external valve trigger controls an internal valve gate. Still another object of this invention is to provide a back-flow valve and valve trigger which provide a relatively short back-flow interval during each filter cycle. Another object of this invention is to provide a back-flow valve and valve trigger which require only intermittent use of the back-flow system during the normal vacuuming process. An additional object of this invention is to provide a back-flow valve and valve trigger which are relatively simple and inexpensive. And it is an object of this invention to provide a back-flow valve and valve trigger which require operation of the blower only during the back-flow process.
A valve and a valve trigger are provided which cyclically connect a vacuum and a blower to a filter. The valve has a box with three openings. The first opening is connectable to the vacuum. The second opening is connectable to the blower. The third opening is connectable to the filter. A gate within the box is adapted to be biased by the blower and the vacuum to close the first opening. The gate is held against the bias by the external trigger to close the second opening. The external trigger is intermittently operated and is adapted to intervally release the internal gate to the bias to close the first opening and open the second opening. The preferred gate is a flapper hinged for angular motion between the first and second openings. The preferred trigger is a rotating cam with a follower fixed to the flapper. The cam operation is controlled by a timer. As the cam perimeter remains engaged with the follower, the flapper is held against the bias to close the second opening. An irregularity in the perimeter of the cam intermittently disengages the cam from the follower and releases the flapper to the bias of the air flow, allowing the flapper to slam against and close the first opening and open the second opening. The blower is energized in response to the timer so that it operates only when the cam is rotating.
A plurality of valves can be combined with a single trigger in a system for cyclically connecting a plurality of filters to the vacuum and the blower. In the preferred system, a plurality of cam followers are equally angularly displaced along the perimeter of a circular cam. The cam irregularity is shaped to release each gate for approximately {fraction (1/12)} rotation of the cam and intervally releases the gates to the bias to sequentially close their first openings.